The present invention relates to a method for cutting the surface of a workpiece in which a cooling fluid is supplied to the cutting area. More particularly, the invention relates to a method for hard turning of workpieces with a Rockwell hardness of 50 HRC or above with ceramic or CBN (cubic boron nitride) tools with a cutting edge having a Vickers hardness of 1700 HV or above. In this description the expression xe2x80x9chard turningxe2x80x9d means turning of carbon steel through or surface hardened to a Rockwell hardness of  greater than 50 HRC and/or with martensitic or bainitic microstructure. As an example the invention may be used for cutting a race surface of a bearing which is in rolling contact with rolling elements.
Today, all hard turning with ceramic or CBN tools is performed dry or with low-pressure flood cooling. All known recommendations say that it is very important to keep a high temperature in the cutting zone in order to achieve a good tool life and production economy.
The research work performed according to the invention shows that this is not really true. A primary object of the invention has been to provide a method of hard cutting by which the tool life is increased, higher cutting speed and a better control of the chip shape are obtained.
According to the present invention it has surprisingly shown that when applying a high-pressure jet of cooling fluid just into the gap between the clearance face of a tool and the workpiece material, a number of important advantages are obtained as will be described below.
The method generally entails using high pressures. The cooling fluid, just before leaving the jet nozzle, having a pressure from 60, preferably 120 to about 400 bar.
According to one aspect, the present invention provides a method for cutting or hard turning the surface of a workpiece using a cutting tool comprising supplying a cooling fluid to a cutting area, wherein in that the cooling fluid is supplied as a jet with high pressure leaving the jet nozzle with a pressure above 60 bar.
The method according to the invention further includes hard turning of workpieces with a Rockwell-hardness of 50 HRC or above using a cutting tool with a cutting edge comprising any material being harder than 1700 HV, especially Al2O3 or CBN (cubic boron nitride) with a Vicker hardness above 1700 HV, preferably above 2800 HV. Examples of suitable cooling fluids include water and carbon dioxide.
According to another aspect of the invention the cooling fluid is applied simultaneously to the gap between the chip and a rake face of the tool and between the clearance face of the tool and the work material.